Metal-atom penetration and diffusion in organic solids: difference between σ- and π- orbital molecular systems

Abstract

The penetration and diffusion of metal atoms in self-assembled monolayers (SAMs) and pentacene solids were studied by first-principles calculations. It was shown in the case of SAM that metal atoms easily penetrate and diffuse in solids, reflecting the weak interaction between metal atoms and molecules. Even when diffusing metal atoms produce a cluster, such a cluster can easily diffuse in solids. In the case of pentacene, on the other hand, since the interaction between metal atoms and molecules is attractive and strong, metal atoms actively enter into solids and are tightly bonded to molecules. We found that Au atoms prefer to produce a cluster at the molecule edge and such a cluster is difficult to move, while Al atoms are scatteringly distributed and last the diffusion owing to the repulsive interaction between Al atoms. We showed that the difference in metal-atom behavior comes from the difference in electronic structure between SAM and pentacene, which are, respectively, σ- and π-orbital molecular systems.